Spondylolisthesis correction apparatus and method

ABSTRACT

An apparatus and method are provided that allow for the realignment and stabilization of adjacent vertebrae. An implant of this invention both repositions adjacent vertebrae and remains in situ to maintain the new position. The implant has two halves which are interlocked such that they can slide horizontally with respect to each other. Movement of the implant halves and their respective positions are controlled by set screw within the implant. The implant includes radial anchors which fit into alignment slots made in the misaligned vertebra by the disclosed method. The set screws are used to advance the halves of the implant which in turn move the misaligned vertebrae back into correct positions. The correct position of the vertebrae is locked in place through a nut and a plate.

FIELD OF INVENTION

The present inventions relates generally to the correction ofspondylolisthesis and other spinal column injuries or deformities in thefields of neurosurgery and orthopedics. More specifically, the inventionis used for the stabilization of repositioned vertebral bodies.

BACKGROUND OF THE INVENTION

Spondylolisthesis is a medical condition in which one vertebra slipsforward in relation to an adjacent vertebra usually in the lumbar regionof the spine. This condition can cause symptoms that include pain in thelow back, thighs, and/or legs, muscle spasms, weakness, and/or tighthamstring muscles while in some cases only radiographic imaging revealsthe condition.

To correct this condition and other similar conditions of vertebraldislocation, the only effective long-term curative treatment isreconstructive surgery and fusion of the affected vertebra to itsadjacent neighbor. Vertebral fusion is generally accomplished by fixingapparatus to and between vertebrae. In addition to the stabilization andcorrection of spondylolisthesis, other spinal conditions may be:stabilization of fractures, correction of spinal deformities (e.g.scoliosis, kyphosis), stabilization and correction of degenerativespinal lesions and narrow spinal canal, reconstruction after tumorresection, and secondary spinal surgery.

The novel method and implant discussed herein allows for the correctionof spondylolisthesis by movement of the vertebrae into better alignmentwhile maintaining stabilization of the vertebrae in the new position inorder for the spinal fusion to be completed by ossification.Specifically, the implant is used to move the vertebrae into apost-surgical position and keep the vertebrae in the post-surgicalposition during the ossification process.

Roggenbuck in U.S. Pat. No. 6,491,695 discloses the use of an apparatusand method for aligning vertebrae which involves creating a helicalthreaded surface in endcaps of the vertebrae and then threading apositioning device into position to align the vertebrae. Once thevertebrae are positioned, the positioning device is removed and animplant is inserted to maintain the vertebrae in position.

Ray in U.S. Pat. No. 6,582,431 discloses the use of an expandablenon-threaded spinal fusion device which requires the vertebrae to bemoved into correct position before the device can be inserted andimplanted.

Betz in U.S. Pat. No. 6,533,791 discloses a device for stabilization ofthe lumbar spinal column which requires cutting helical thread marksinto the vertebrae that are to be repositioned and then installing animplant to maintain the position. The repositioning device does not stayin the body after the surgery but instead an implant must be inserted tomaintain the repositioning.

Therefore, there is a need in the art to combine an implant with arepositioning device in order to reduce the possible repositioning ofthe vertebrae. There is a further need in the art to provide foradjustment of the vertebrae after an implant has been installed.

SUMMARY OF INVENTION

Disclosed is an apparatus and method for aligning vertebrae due toslippage of the vertebrae relative to each other. To this end, a methodand apparatus is disclosed for placing a novel implant between twovertebrae which will move the vertebrae into proper alignment andmaintain that alignment until ossification can occur. The implantdisclosed is left in situ once the vertebrae have been repositioned. Theimplant disclosed also provides support for the effected vertebraesuperior to that of previous methods known in the prior art. The implantalso allows for fine adjustments and post implantation adjustments ofthe vertebrae superior to that of the prior art.

The disclosed method includes approaching the vertebra anteriorly andremoving a portion of vertebral disk between the misaligned vertebrae.Known interbody spacers are then inserted between the vertebrae untilthe proper restorative height is achieved. The spacers are removed and adistractor is placed between the vertebrae in order to guide thesubsequent placement of the implant. A novel gate is inserted over anovel distractor to properly guide a novel saw mechanism to cut into thevertebrae at precise locations and allow for the insertion of a novelimplant. Different gates are provided depending on the necessaryrestorative height to be achieved and amount of slip between thevertebrae.

The disclosed implant has two halves which include a dovetail groovesystem which locks the two halves together but allows them to slide withrespect to each other along their longitudinal axis. The implant hasradial anchors which extend from each half and which fit into slots inthe vertebrae cut by the saw. The implant includes a drive bolt whichengages the two halves and which, when turned, slides one half of theimplant in relation to the other. The advancing halves of the implantcarry the radial anchors with them that align the vertebrae. Dependingon the amount of slip between the vertebrae and the necessaryrestorative height, different sized implants and associated tools may beused.

The implant is inserted through a distractor by use of an inserter. Thehalves of the implant are aligned so that the radial anchors correspondto slots made in the misaligned vertebrae. The implant is rotated intoplace by the inserter such that the radial anchors fit securely in theslots previously made by the saw in the vertebrae. The distractor isthen removed.

In the case of anterior listhesis of the superior vertebra, the drivebolt of the implant is then rotated so that the upper half of theimplant is advanced posteriorly. The superior vertebra is pulledposteriorly with respect to the inferior vertebra by the movement of theupper half of the implant with respect to the lower half.

The position of the implant is locked into place by use of anarticulating combination of a nut and a plate, thereby maintainingalignment of the vertebrae. The nut and plate can be removed, allowingfor post-surgical adjustment of the implant.

BRIEF DESCRIPTION OF DRAWINGS

The disclosed inventions will be described with reference to theaccompanying drawings, which show important sample embodiments of theinvention and which are incorporated in the specification hereof byreference, wherein:

FIG. 1 is a side view of a section of human spine characterized by aspondylolisthesis condition.

FIG. 2 is an isometric view of a distractor of a preferred embodiment ofthe invention.

FIG. 3 a is an isometric view of an impactor of a preferred embodimentof the invention.

FIG. 3 b is an isometric view of an impactor in conjunction with adistractor of a preferred embodiment of the invention.

FIG. 4 is a side view of a section of a human spine with the distractorin place between vertebrae.

FIG. 5 a is a partial isometric view of a gate of a preferred embodimentof the invention.

FIG. 5 b is a plan view of a gate of a preferred embodiment of theinvention.

FIG. 5 c is an elevated view of a gate of a preferred embodiment of theinvention.

FIG. 6 is an exploded isometric view of a saw of a preferred embodimentof the invention.

FIG. 7 a is a partial plan view of the relational section of the saw ofa preferred embodiment of the invention.

FIG. 7 b is a partial isometric view of the spindle shaft of a preferredembodiment of the invention.

FIG. 7 c is a partial side view of the spindle shaft of a preferredembodiment of the invention.

FIG. 8 a is an end view of the saw with the saw blade in a loweredposition of a preferred embodiment of the invention.

FIG. 8 b is an end view of the saw with the saw blade in a raisedposition of a preferred embodiment of the invention.

FIG. 9 is a cut away side view of section of a human spine with thedistractor, gate, and saw in place between the vertebrae.

FIG. 10 is an exploded isometric view of the implant of a preferredembodiment of the invention.

FIG. 11 is an isometric view of the implant of a preferred embodiment ofthe invention.

FIG. 12 is an isometric view of the implant in an extended position of apreferred embodiment of the invention.

FIG. 13 a is an end view of the inserter of a preferred embodiment ofthe invention.

FIG. 13 b is an isometric view of the inserter of a preferred embodimentof the invention.

FIG. 14 is a partial isometric view of the inserter and the implant of apreferred embodiment of the invention prior to attachment.

FIG. 15 is an isometric view of a guide block of a preferred embodimentof the invention.

FIG. 16 is a cut away side view of a section of a human spine and animplant during positioning by an inserter of a preferred embodiment ofthe invention.

FIG. 17 is a cut away side view of a section of a human spine and animplant in place prior to the alignment of the vertebrae.

FIG. 18 is an isometric view of a nut of a preferred embodiment of theinvention.

FIG. 19 a is an isometric view of a plate of a preferred embodiment ofthe invention.

FIG. 19 b is a cut away side of a plate of a preferred embodiment of theinvention.

FIG. 20 is a cut away side view of a section of a human spine with animplant in a retracted position and a nut and a bolt in place.

FIG. 21 is a cut away side view of a saw in an alternate saw embodiment.

FIG. 22 a is a cut away side view of the end of saw in an alternateembodiment of the invention.

FIG. 22 b is an end view of the end of an alternate saw embodiment.

FIG. 23 a is a top view of the top of the chuck of an alternate sawembodiment.

FIG. 23 b is a partial cut away side view of the chuck of an alternatesaw embodiment.

FIG. 24 a is a side view of an implant in another embodiment of theinvention.

FIG. 24 b is an end view of an implant in another embodiment of theinvention.

FIG. 25 is an isometric view of an impactor in conjunction with adistractor of another embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is an illustration of a lumbar spine in a patient who hascontracted spondylolisthesis. The vertebrae 10 are separated byvertebral disk 50. As a result of advanced spondylolisthesis, superiorvertebra 20 slips forward in relation to the next inferior vertebra 40and causes distended disk 70. To repair slippage of the vertebrae,superior vertebra 20 and inferior vertebra 40 are realigned and fusedtogether. To accomplish this, a portion of distended disk 70 is removedand replaced with an implant which maintains realignment and supportsthe spine until ossification occurs whereby superior vertebra 20 andinferior vertebra 40 are permanently fused.

In order to assure proper alignment, a magnetic resonance image (“MRI”)or plain lateral radiographs are used to observe the supine position tomeasure the severity of the spondylolisthesis condition prior tosurgery. The restorative height of the interbody space after partialremoval of distended disk 70 and the necessary amount of re-alignmentcan be estimated by review of the MRI or plain lateral radiographs. Theimplant size can be determined by the estimates.

The present invention uses the anterior surgical approach to the lumbarspine in order to reach the vertebrae that will receive the implant. Theanterior surgical approach to the lumbar spine is understood in the artand is not discussed in detail here.

Referring still to FIG. 1, once the lumbar spine is exposed to thesurgeon, superior vertebra 20, inferior vertebra 40, and distended disk70 are located and identified. A standard marking pin known in the artis inserted into distended disk 70 at the putative midline and left inplace.

The implant should be optimally placed at the midline in the sagitalplane. Lateral radiographs or x-rays are utilized to confirm theappropriate surgical level and anterior-posterior x-ray imagingdemonstrates the midline relative to the marking pin. Once confirmed,the midline of distended disk 70 is marked on distended disk 70 by useof generally accepted marking means. The marking pin is then removed.

Portion of distended disk 70 is removed. Boundaries of generousrectangular annulatomy are created in distended disk 70 by use ofscalpel. The size of the annulatomy will depend upon the size of theimplant and allows additional space on either side of implant to allowinterbody arthodesis on both sides of implant after implant is deployed.The width of annulatomy will be in the range of between about 2 cm andabout 5 cm. Portion of distended disk 70 within the boundary ofannulatomy is removed by use of rongeurs and curettes.

Vertebral endplate preparation is performed in standard fashion as knownin the art while maintaining cortical endplate integrity centrally.Anterior osteophytes may also be removed from the ventral aspect of thevertebral bodies during this stage of the surgery.

In order to gain the appropriate restorative height between superiorvertebra 20 and inferior vertebra 40, sequentially larger interbodyspreaders are impacted into the rectangular annulotomy in distended disk70 until optimal height restoration is achieved. Interbody spreaders areknown in the art. When optimal height restoration is achieved, interbodyspreaders are removed and appropriate height distractor 110 is inserted.

FIG. 2 illustrates one embodiment of distractor 110. Distractor 110 ismade of titanium, stainless steel, or other commercially availablematerial which is easily sterilized. Rigid plastics can be used such aspolyvinyl chloride (PVC) in disposable embodiments. Distractor 110 isrectangular in cross-section and includes hollow distractor channel 115.Distractor channel 115 is rectangular in cross-section and runs thelength of distractor 110. The dimensions of distractor 110 varydepending on the optimal height restoration to be achieved, but heightof distractor 110 should generally range between about 0.5 cm and about1.5 cm and the width of distractor 110 should range between about 2 cmand about 5 cm. The length of distractor 110 is between about 30 cm andabout 60 cm. The thickness of walls of distractor 110 should rangebetween about 1 mm and about 5 mm depending on the material ofconstruction to achieve a rigid structure. The dimensions of distractorchannel 115 should range between about 0.4 cm and about 1.4 cm high,about 1.9 cm and about 4.9 cm wide.

Posterior end of distractor 110 contains distractor arm 117 anddistractor arm 118. Distractor arm 117 extends longitudinally from side80 of distractor 110. Distractor arm 117 includes distractor point guide246 having angled surfaces 253 and 254. Opposing angled surfaces 253 and254 is distractor stop 119. Distractor arm 118 extends longitudinallyfrom the side 81 of distractor 110 and includes distractor point guide256 having rounded surfaces 258 and 255. Opposing rounded surfaces 258and 255 is distractor stop 122. The height of distractor arm 117 anddistractor arm 118 are approximately the same as the height ofdistractor 110. The width of distractor arm 117 and distractor arm 118are between about 0.5 mm and about 1 mm. The width of the distractorarms should provide rigidity with respect to the body of the distractor.Distractor arm 118 and distractor arm 117 form implant hollow 130. Endgap 120 is formed at the forward end of implant hollow 130. Thepreferred design of end gap 120 is between about about 1.7 cm and about4.7 cm. Distractor stop 122 and distractor stop 119 are between about0.5 mm and about 2 mm in length.

Torque handle 235 is rigidly mounted to distractor body 99. Torquehandle 235 is generally in the range of about 2 cm to about 5 cm inlength with a diameter in the range of about 0.5 cm to about 2 cm. Thepreferred location of torque handle 235 is approximately between ¼ to ½from the anterior end 111 of distractor 110. A set of distractorgraticules 135 are etched at 1 mm intervals on the side of distractor110 along the outside of distractor arm 118 and distractor arm 117.

In the preferred embodiment, the cross-sectional height and width ofdistractor 110 may vary. In its preferred use, a set of variable heightdistractors is provided so that the distractor height which matches thevertical distance between the vertebrae may be used during surgery. Thepreferred set of heights preferably varies in one millimeter incrementsbetween about 5 mm and about 2 cm.

FIG. 3 a illustrates the preferred embodiment of impactor 140. Impactor140 includes impactor handle 170 which is cylindrical with a diameter inthe range of about 0.3 cm and about 2 cm. The length of impactor handle170 ranges between about 5 cm and about 25 cm. In one embodiment,impactor handle 170 is etched with impactor centerline 165 across itsdiameter. Impactor centerline 165 is parallel to the longcross-sectional axis of impactor body 160.

Impactor body 160 is formed integrally with impactor handle 170.Impactor body 160 is rectangular in cross-section and sized to fitwithin distractor channel 115 without excessive play. In the preferredembodiment, the impactor body is sized to allow for approximately 0.3 mmplay between the exterior of the impactor body and the distractorchannel.

Angled section 141 extends from impactor handle 170 to impactor body 160at an angle between about 25 and about 65 degrees. Angled section 141serves to center the impactor handle with respect to the impactor bodyand distribute impact loads from the impactor handle to the impactorbody as will be further described. The preferred length of impactor body160 should range between about 30 cm and about 45 cm. The posterior endof impactor body 160 includes impactor seat 150 integrally formed withimpactor body 160. Impactor seat 150 is sized and shaped to fit withinend gap 120 shown in FIG. 2. Impactor seat 150 has rounded surface 155.On either side of impactor seat 150 are stop surface 152 and stopsurface 153. Impactor 140 is preferably made from titanium, stainlesssteel, or other materials which are readily sterilized or from a rigidplastic such as PVC which may be disposed of after use.

Other cross-sectional shapes of the impactor and distractor are alsoacceptable, such as elliptical, as long as the impactor fits inside thedistractor channel such that it can move longitudinally in distractorchannel 115 without rotation and without significant “play” or angulardisplacement.

In use, impactor 140 is placed inside distractor channel 115, such thatimpactor seat 150 fits into end gap 120 as shown in FIG. 3 b. Impactorcenterline 165 is aligned with the anatomical midline marked previously.Distractor 110 and impactor 140 are aligned with the anatomical midlineand inserted into the rectangular annulatomy in distended disk 70. Amallet is used to tap impactor 140 and distractor 110 into the midlinesagital plane under fluoroscopic guidance until posterior edge ofdistractor 110 reaches the dorsal epiphyseal ring on the ventrallysuperior vertebra 20. Impactor 140 is then withdrawn from distractorchannel 115 and distractor 110 is left in situ.

In the preferred embodiment, impactor 140 is also provided in a set ofvariable sizes to match the set of variable sizes of distractor 110, aspreviously described.

FIG. 4 shows distractor 110 in situ between superior vertebra 20 andinferior vertebra 40. Distractor 110 is between superior vertebra 20 andinferior vertebra 40. Once in position, distractor graticules 135 areused to gauge the amount of slip existing between superior vertebra 20and inferior vertebra 40.

FIGS. 5 a, 5 b and 5 c illustrate an embodiment of gate 180. Gate 180has a gate body 223 bordered by side wall 271, bottom side 269, sidewall 284 and top side 268. The gate body also includes saw end 249 anddistractor end 251. In the preferred embodiment, gate 180 has a lengthof between about 5 cm and about 10 cm, a width of between about 2.2 cmand 5.8 cm and a height of between about 0.7 cm and about 2.9 cm.

Gate 180 is provided with saw guide 220 and saw guide 230. Saw guides220 and 230 are a pair of slots which are situated approximately thecenter of top side 268 to the center of side wall 284, encompassingapproximately ¼ of the perimeter of gate body 223. The pair of sawguides are in parallel planes. Saw guide 220 and saw guide 230 terminatein handle guide 257. Handle guide 257 forms a slot generally in thecenter of side wall 284. Handle guide 257 is provided with handle stop252. The width of saw guides 220 and 230 and handle guide 257 in thepreferred embodiment is between about 0.5 cm and 1.5 cm.

Gate body 223 is also provided with saw guide 200 and saw guide 210. Sawguides 200 and 210 are a matched pair of slots which are situatedapproximately the center of bottom side 269 to the center of side wall271, encompassing approximately ¼ of the perimeter of gate body 223. Thepair of saw guides are in parallel planes. Saw guide 200 and saw guide210 terminate in handle guide 240. Handle guide 240 forms a slotgenerally in the center of side wall 271. Handle guide 240 is providedwith handle stop 242. The width of saw guide 200, saw guide 210 andhandle guide 240 in preferred embodiment is between about 0.5 cm andabout 1.5 cm.

Saw guide 220, saw guide 230 and handle guide 257 are ductedlyconnected. Saw guide 220 and saw guide 230 are on centers of betweenabout 0.5 cm to 3.5 cm in the preferred embodiment. Further, saw guide220 is approximately 0.9 cm from saw end 249.

Saw guide 210, saw guide 200 and handle guide 240 are ductedlyconnected. Saw guide 210 and saw guide 200 are on centers of betweenabout 0.5 cm to 3.5 cm in the preferred embodiment. Further, saw guide210 is approximately 1.9 cm from saw end 249.

Gate body 223 is further provided with interior channel 195 which islongitudinally centered within gate body 223. Interior channel 195includes saw entrance 247. Saw entrance 247 in the preferred embodimenthas dimensions slightly larger than guide body 310 which will bedescribed in more detail with respect to FIG. 6. The diameter of sawentrance 247 is maintained by interior channel 195 from saw entrance 247until gate lip 185. At gate lip 185, interior channel 195 increases inheight and width to accommodate the exterior of distractor 110. Thedimensions of interior channel 195 remain constant from gate lip 185 todistractor end 251 terminating in distractor entrance 248.

In one embodiment, gate 180 can also include raised indicator arrow 245or other visual aid or tactile indicator to indicate which end of gate180 is to be inserted over distractor 110.

In the preferred embodiment, many gates are provided in a kit duringsurgery. The gates each have saw guides that are spaced apart atdifferent lengths with respect to the top and the bottom of each gate.The different spacings correspond to different distances that thevertebrae have slipped. In one preferred embodiment, in the less severecases, saw guides 230 and 220 will be offset from saw guides 200 and 210by about 1 mm. The offset between saw guides 230 and 220 and saw guides200 and 210 will increase by 2 mm increments. In more severe cases, theamount of slip will be more pronounced and the offset can beapproximately 20 mm. Position of saw guides 200 and 210 on gate 180 willstay constant. The gates also vary in height to match the variableheight of the distractor.

Referring now to FIGS. 6 and 7 a, an embodiment of saw 250 can be seen.Saw 250 includes saw handle 260 to conical section 262. Conical section262 is connected to handle post 265. Handle post 265 integrally supportssaw guide post 270. Saw guide post 270 is perpendicular to thelongitudinal axis of saw 250. Handle post 265 includes abutment surface272 narrows to the diameter of spindle shaft 273. Abutment surface 272connects spindle shaft 273 with blade seating shoulder 275. Bladeseating shoulder 275 is flat surface 276 and semicircular section 277.Blade seating shoulder 275 is connected to bolt 295. Bolt 295 hasthreaded section 296 which is directly adjacent to flat surface 276 andsemicircular section 277. Bolt 295 has a threaded section 296 and a flatsurface 297.

Saw 250 includes guide body 310. Guide body 310 includes a rectangularsection 311 and an angular section 312. Rectangular section 311 in thepreferred embodiment is sized to fit within saw entrance 247 as shown inFIG. 5 b and distractor channel 115 shown in FIG. 2. The rectangularsection tolerance must be such that rectangular section 311 slideslongitudinally with respect to distractor channel 115 and interiorchannel 195 without significant angular play about the longitudinalaxis. In the preferred embodiment, these tolerances are approximately0.3 mm. Angular section 312 connects to flat surface 313. Guide body 310also includes spindle hole 301 which traverses the longitudinal axis ofguide body 310 and is sized to fit around spindle shaft 273. Spindlehole 301 is sized to allow rotation with respect to spindle shaft 273.

Rectangular section 311 includes spacer 300, saw alignment stop 281 andsaw alignment stop 279. As can be seen best in FIG. 7 a and FIG. 6, sawalignment stop 281 includes a horizontal surface 282. Saw alignment stop279 includes vertical surface 283.

When assembled, saw 250 provides for 90 degrees rotation of saw handle260 with respect to guide body 310. Thrust bearing 302 rests adjacentabutment surface 272. Guide body 310 rests on spindle shaft 273 viaspindle hole 301. Flat surface 313 is adjacent angular section 312 andthrust bearing 302 providing a bearing surface between abutment surface272 and flat surface 313. Thrust bearing 278 resides around semicircularsection 277 of blade seating shoulder 275 adjacent vertical end 315 ofrectangular section 311. Locking hole 285 of saw blade 280 is adjacentflat surface 276 and semicircular section 277 of blade seating shoulder275. Locking hole 285 includes flat surface 316 which when brought intocontact with flat surface 276, prevents rotation of saw blade 280 withrespect to blade seating shoulder 275, consequently, with respect to sawhandle 260. Lock nut 290 is threaded onto threaded section 296 of bolt295. Flat surface 276, flat surface 316 and saw alignment stop 281 areparallel with the axis of saw guide post 270.

Saw 250 and all its components are made from titanium, stainless steel,or other material which is used with surgical tools and equipment. Inthe preferred embodiment, rectangular section 311 of saw 250 is providedin several sizes in a set of several sizes to match the sizes of thedistractor 110, as previously described. Alternatively, a set of severalsaws 250 is provided, each having a rectangular section 311 whosecross-section is sized to match the distractor channel 115 of the set ofdistractors 110. In addition, a set of blades may be provided eachhaving different dimensions to achieve different lumbar dimensions.

FIGS. 8 a and 8 b are end views of saw 250. FIG. 8 a illustrates sawblade 280 in lowered position. In lowered position, saw blade 280 isflush with guide body 310. FIG. 8 b illustrates saw blade 280 in raisedposition. In raised position, saw blade 280 is perpendicular to guidebody 310.

In the preferred embodiment, saw blade 280 is between 0.9 cm and 4.9 cmlong with a width of between 1 mm and 5 mm. Saw blade 280 has a flatbottom and two curved ends 303 and 305. Saw blade 280 includes a lockinghole 285 of approximate diameter and shape as bolt 295. Curved end 305includes saw teeth 304 having a height of about 0.5 mm and about 1.5 mm.Saw blade 280 also includes notches 317 and 318. As shown in FIG. 8 b,saw blade 280 in its raised position rests adjacent vertical surface 283which prevents it from rotating counterclockwise. In lowered position,as shown in FIG. 8 a, notch 318 rests adjacent horizontal surface 282and prevents rotation of the saw blade clockwise.

Referring now to FIG. 9, in use, gate 180 is placed over the anteriorend of distractor 110 and advanced until anterior end 111 rests againstgate lip 185. Saw 250 is placed in lowered position. Rectangular section311 is placed in interior channel 195 and advanced through distractorchannel 115 until spacer 300 reaches distractor stop 122 or saw guidepost 270 reaches handle stop 242.

In use, the saw is used to make two sets of receiving notches in theupper and lower vertebrae that correspond to the positions of the sawguides. More particularly, saw 250 is retracted until saw guide post 270is directly adjacent saw guide 230. Saw handle 260 is rotated clockwise90 degrees such that saw guide post 270 advances through saw guide 230on gate 180. Rotation of saw handle 260 will rotate saw blade 280causing it to cut into superior vertebra 20 thereby forming a slot 900.Distractor torque handle 235 is grasped to apply counter torque andprevent rotation of the saw from displacing distractor 110 angularlywith respect to the effected vertebrae. Saw handle 260 is then rotatedcounterclockwise positioning saw guide post 270 in handle guide 257. Saw250 is then extracted such that saw guide post 270 is adjacent saw guide220. Saw handle 260 is then rotated clockwise 90 degrees such that sawguide post 270 advances into saw guide 220. Rotation of saw handle 260rotates saw blade 280 thereby cutting into superior vertebra 20 andforming slot 902. Saw guide post 270 is then rotated counter-clockwiseso that saw guide post 270 resides in handle guide 257.

Saw blade 280 is placed in its lowered position. Saw 250 is then removedfrom distractor channel 115 through interior channel 195. Saw 250 isthen rotated 180 degrees about its axis and rectangular section 311replaced is in interior channel 195 of gate 180. Saw 250 is furtherreinserted into distractor channel 115.

Saw guide post 270 is adjacent saw guide 210. The saw handle is rotatedclockwise 90 degrees such that saw guide post 270 enters saw guide 210.Rotation of saw handle 260 consequently rotates saw blade 280 exposingsaw teeth 304 to inferior vertebra 40 thereby cutting into inferiorvertebrae 40 thereby forming slot 903. Distractor torque handle 235 isused to apply counter torque and prevent the saw rotation fromdisplacing distractor 110. Saw handle 260 is then rotated clockwise suchthat saw guide post 270 advances through the saw guide and into handleguide 240. Saw 250 is then extracted such that saw guide post 270advances through handle guide 240 until it is adjacent saw guide 200.Saw handle 260 is then rotated 90 degrees such that saw guide post 270advances into saw guide 200. The rotation of saw handle 260 rotates sawblade 280 causing a second cut into inferior vertebra 40 thereby formingslot 904.

Saw 250 is removed through distractor channel 115 and interior channel195. Gate 180 is then removed from the anterior end of distractor 110.

Slots 900, 902, 903 and 904 in superior vertebra 20 and inferiorvertebra 40 are substantially consistent with the spacing on gate 180between saw guides 200, 210, 220, and 230, respectively.

The novel implant is then prepared to be inserted.

Referring to FIGS. 10, 11 and 12, implant 320 is described. Implant 320is comprised of two semi-cylindrical halves, upper half 340 and lowerhalf 330. Lower half 330 includes parallel radially exposed and planarradial anchors 264 and 261. The radial anchors are integrally formedwith upper half 340. Radial anchor 264 further includes curved surface266. Radial anchor 261 includes curved surface 263.

Lower half 330 includes two parallel planar radial anchors 370 and 371.Radial anchors 370 and 371 are integrally formed with lower half 330.Radial anchor 370 includes curved surface 372. Radial anchor 371includes curved surface 373.

Upper half 340 includes upper threaded collar 345. Lower half 330includes lower threaded collar 355. The exterior of the upper halfincludes index marks 360. Index marks 360 correspond with index marks361 on lower half 330.

Upper half 340 includes upper channel 380 which is threaded. Lower half330 includes lower channel 390. Lower channel 390 is not threaded. Upperhalf 340 is joined to lower half 330 with a mating interconnectionbetween dovetail guide 386 and dovetail guide 385 found on upper half340 and dovetail slot 396 and dovetail slot 395, respectively, locatedon lower half 330.

Lower half 330 includes set screw stop 400 integrally formed with lowerhalf 330 and residing within lower channel 390. Set screw stop 400 issolid plug which fills lower channel 390 beyond end of set screw 350.

Lower half 330 includes set screw step 392. Set screw step 392 extendsinto upper channel 380 and in upper half 340 and lower channel 390 inlower half 330. Set screw step 392 decreases diameter of upper channel380 and lower channel 390 by approximately 2 mm.

As can best be seen in FIG. 12, when assembled, upper half 340 and lowerhalf 330 of implant 320 are engaged in a sliding relationship providedby the dovetail guides 385 and 386 residing in dovetail slots 395 and396. As can be seen in FIG. 11, when assembled, upper half 340 and lowerhalf 330 form implant body 346. Radial anchor 264 is aligned with radialanchor 370. Radial anchor 261 is aligned with radial anchor 371.Furthermore, upper threaded collar 345 and lower threaded collar 355 arealigned and form a cylindrical threaded attachment collar 356.

In use, set screw 350 can be rotated either counter-clockwise orclockwise within lower channel 390 and upper channel 380. The set screwis retained in position by set screw stop 400 and set screw step 392. Asset screw 350 is rotated, threads 351 engage the threads on upperchannel 380 and slide upper half 340 with respect to lower half 330. Asupper half 340 and lower half 330 are displaced, radial anchors 264 and261 are displaced with respect to radial anchors 370 and 371 along thelongitudinal axis of implant 320.

Implant 320 in the preferred embodiment is made from titanium, stainlesssteel, alloys such as titanium allow, or other materials which areeasily sterilizable. Implant 320 or parts thereof, may also be made fromcomposite materials such as synthetic bone. Some composites or syntheticbone products include demineralized bone matrix, collagen, ceramics,cements, and polymers, such as silicone and some acrylics and includeproducts such as Vitoss, Cortoss, Rhakoss, Pro Osteon, and Gu-Bang.

In the preferred embodiment, implant body 346 is between about 0.5 cm toabout 2.5 cm in diameter and between about 2.0 cm and about 4.5 cm inlength. In the preferred embodiment, cylindrical threaded attachmentcollar 356 is between about 0.4 to about 2.4 cm in diameter and betweenabout 0.5 and 2.0 cm in length. In the preferred embodiment, radialanchors 264, 261, 370 and 371 have a height (as measured from the centerplane of the implant) of between about 0.5 cm and about 3.5 cm with anaspect ratio of ½ to ½ between radial anchors 264, 261, 370, and 371 anddiameter of implant body 346.

In the preferred embodiment, upper half 340 includes exactly two radialanchors and lower half 330 includes exactly two radial anchors. However,in other embodiments, the upper half and lower half of the implant mayinclude more or less than two radial anchors. Furthermore, the upperhalf and lower half of implant 320 do not necessarily need to includethe same number of radial anchors. In embodiments which includedifferent numbers of radial anchors, it will be understood by thoseskilled in the art that the same number of saw guides must be includedon gate 180 in order to correspond with the number and orientation ofthe radial anchors.

FIGS. 13 a and 13 b illustrate inserter 430. Inserter 430 includes upperhalf 440 and lower half 450. Upper half 440 includes upper hexagonalsection 441 and upper cylindrical section 442. Within upper cylindricalsection 442 resides upper dovetail guide 454. Adjacent upper dovetailguide 454 is implant channel 446. Implant channel 446 includes lockingthread 445.

Lower half 450 includes lower hexagonal section 451 and lowercylindrical section 453. Lower cylindrical section 453 includes lowerdovetail channel 452. Upper dovetail guide 454 fits within lowerdovetail channel 452 and allows for sliding movement between upper half440 and lower half 450. As can best be seen in FIG. 13 b, when upperhalf 440 and lower half 450 are assembled, inserter 430 assumes an outercircular perimeter. In the preferred embodiment, this outer circularperimeter is sized to fit within distractor channel 115, shown in FIG.2, with sufficient clearance to allow for rotation of inserter 430.Further, in the preferred embodiment, the hexagonal shape of upper half440 and lower half 450 and inserter 430 is sized to allow for rotationwith a tool such as a spanner wrench. In the preferred embodiment, thelength of inserter 430 is sufficient to span the length of distractorbody 99.

Locking thread 445 is sized to mate with upper threaded collar 345 onimplant 320 as shown in FIGS. 10, 11 and 12.

Referring to FIG. 15, guide block 460 will be described. Guide block 460includes guide block bottom 465 and guide block top 475. Guide block 460also includes guide hole 470 which is centrally located within the guideblock and spans its length. Guide block bottom 465 is sized to fitwithin distractor channel 115. Guide block top 475 is sized so that itwill not fit within distractor channel 115 but rather abut anterior end111 of distractor body 99 (as shown in FIG. 2).

In use, inserter 430 is used to place the implant in position betweenthe affected vertebra and rotated into position. More particularly thento implant the implant, the amount of offset calculated according to theradiograph is reduced to a number of millimeters. The implant isadjusted using upper adjustment index marks 360 and lower adjustmentindex marks 361 to an offset position using set screw 350. The amount ofoffset can be observed by observing the offset between index marks 360and 361. In an alternate embodiment, the offset can be derived bycalculating the number of rotations of the set screw and multiplying bythe pitch of the threads. In an alternate embodiment, the pitch of thethreads is set to a convenient number so that a single rotation of theset screw results in a predetermined movement of the upper and lowerhalves, such as 1 mm for example. An example of an offset position isshown in FIG. 12.

In use, inserter 430 is assembled and its cylindrical section is guidedinto and through guide hole 470 until guide block top 475 reaches thehexagonal section of the inserter.

Implant 320 is then connected to inserter 430 as shown in FIG. 14.Locking thread 445 of inserter 430 is engaged with upper threaded collar345 of implant 320. Inserter lower half 450 is advanced towards implant320 whereby dovetail guides 386 and 385 of implant 320 are engaged bylower dovetail channel 452 on inserter 430 thereby securing implant 320to inserter 430.

Referring now to FIG. 16, the process of inserting implant 320 into theaffected vertebra will be described. As previously described, distractor110 is in position between superior vertebra 20 and inferior vertebra40. Implant 320, while attached to inserter 430 is oriented and placedwithin distractor channel 115. Implant 320 is placed in distractorchannel 115 with radial anchors 264 and 261, 370 and 371 positioned sothat clockwise rotation of the implant will result in radial anchor 264and 261 encountering superior vertebra 20 and radial anchor 370 and 371encounter inferior vertebra 40. Using the hexagonal section of inserter430, implant 320 is advanced within distractor channel 115 a sufficientdistance to allow guide block bottom 465 to be inserted into distractorchannel 115. Guide block bottom 465 is advanced within distractorchannel 115 until guide block top abuts anterior end 111 of distractorbody 99.

Implant 320 is then advanced within distractor channel 115 until thehexagonal section of inserter 430 abuts guide block top 475.

The dimensions of guide block top 475 and cylindrical section ofinserter 430 are such that when the hexagonal section of the inserterabuts guide block top 475, implant 320 is in proper position in relationto slots 900, 902, 903 and 904 such that radial anchor 264 is adjacentslot 900, radial anchor 261 is adjacent slot 902, radial anchor 370 isadjacent slot 904 and radial anchor 371 is adjacent slot 903.

Inserter 430 is then rotated 90 degrees clockwise such that the radialanchors are rotated into position in the slots in their respectivevertebrae.

Once in position, implant 320 is released from inserter 430.

The diameter of inserter guide hole 470 should provide sufficientclearance for rotation and transition of cylindrical portion of inserter430 without excessive play. In the preferred embodiment, the diameter ofguide hole 470 should not exceed the diameter of the cylindrical sectionof inserter 430 by more than 0.1 mm.

To release implant 320 from inserter 430, inserter lower half 450 isretracted anteriorly past superior locking thread 445 and disengagesfrom lower dovetail channel on lower cylindrical section 453 of theinserter. Inserter 430 is rotated 180 degrees such that upper threadedcollar 345 is disengaged from locking thread 445 on implant channel 446on the inserter. Inserter 430 and guide block 460 are then removed fromdistractor 110.

Distractor 110 is then removed from between superior vertebra 20 andinferior vertebra 40 by pulling anteriorly.

FIG. 17 illustrates the positioning of implant 320 between superiorvertebra 20 and inferior vertebra 40 after distractor 110 has beenremoved. Upper half 340 is adjacent superior vertebra 20, radial anchor264 is located in slot 900, radial anchor 261 is located in slot 902.Lower half 330 is adjacent inferior vertebra 40 and radial anchor 370 islocated in slot 904. Radial anchor 371 is located in slot 903.

In order to align superior vertebra 20 and inferior vertebra 40, upperhalf 340 and lower half 330 are aligned. A spanner is inserted intospanner slot 405 of implant 320. Set screw 350 is rotated to move lowerimplant half 330 anteriorly and upper implant half 340 posteriorally. Inone embodiment, for each complete 360 degrees turn of the set screw willmove lower half 330 1 mm with respect to upper when alignment of theimplant halves is complete, the threads in upper threaded collar 345 andin lower threaded collar 355 will align. Ideally, alignment of theimplant halves will align the vertebrae.

After alignment of the vertebrae, an interbody arthrodesis is performedon each side of implant 320 and between remaining distended disk 70. Thetechnique for interbody arthrodesis is surgeon's choice from those knowntechniques.

FIGS. 19 a and 19 b illustrates one embodiment of plate 540. Plate 540is selected based on shape and size of individual patient's vertebrae.In one embodiment, the height of plate 540 is between 2.5 cm and 7 cmand the width of plate 540 is between 1.5 cm and 5 cm. Depth of plate540 is between 0.2 cm and 1.5 cm. Plate 540 is slightly concave toapproximate the curvature of inferior vertebra 40 and superior vertebra20.

Plate 540 includes plate nut hole 560 in its approximate center. Thediameter of plate nut hole 560 on the anterior side of plate 540 isbetween 0.65 cm and 3.4 cm while the diameter of plate nut hole 560 onthe posterior side of plate 540 is between 0.45 cm and 2.5 cm.

Plate 540 also includes four holes 550. Each hole 550 should havediameter between about 1 mm and about 9 mm. But these diameters canvary. The plate is secured to the vertebra by stainless steel screws asknown in the art.

Preferably, plate 540 should be made of titanium or stainless steel.

FIG. 18 illustrates one embodiment of nut 500. Nut 500 has nut head 520which is elliptical. Diameter of nut head 520 is between 0.65 cm and 3.4cm preferably. Nut head 520 contains spanner holes 535. Nut body 510 hasdiameter of between 0.5 cm and 2.5 cm. The diameter of nut body 510should be approximately the same as diameter of implant body 346. Thelength of nut body 510 is between 0.2 cm and 6 cm. Nut 500 should beconstruction of titanium or stainless steel. Other rigid materials canbe used. Nut body 510 includes threaded hole 526. Threaded hole 526 isthreaded to match the threads of upper threaded collar 345 and lowerthreaded collar 355 on implant 320.

In use, to help secure implant 320 in position, nut 500 and plate 540are used, as illustrated in FIG. 20. Nut body 510 is placed throughplate nut hole 560. Nut thread 525 of threaded hole 526 is then alignedwith and threaded onto upper threaded collar 345 and lower threadedcollar 355. Nut 500 prevents implant upper half 340 and implant lowerhalf 330 from moving horizontally against each other.

Plate 540 is then properly aligned with the shape of superior vertebra20 and inferior vertebra 40. Corticocancellous screws 570 are placedinto each of the plate screw holes 550 and screwed into the respectivevertebrae by traditional techniques within the field. The difference indiameters between plate nut hole 560 from front to back allowsarticulation of the bolt with respect to the plate. Once plate 540 isattached to superior vertebrae 20 and inferior vertebrae 40 with screws570, and is secured via nut 500 to implant 320 the device acts as amonolithic structure preventing rotational, lateral oranterior/posterior movement of vertebral bodies 20 and 40 with respectto each other, allowing ossification of said vertebral bodies

Surgery is completed by standard anterior approach surgery techniquesand implant is in place.

In the event that adjustments need to be made to implant 320, screws570, nut 500 and plate 540 can be removed and set screw 350 adjustedwith any appropriate spanner head wrench. Nut 500, plate 540 and screws570 are then replaced.

FIGS. 21, 22 a and 22 b illustrate another preferred embodiment of thesaw. FIG. 21 shows saw 802 with mill bit 750. Saw 802 includes handle817 and conical section 814. Interior of handle 817 includes motor 860.Motor 860 is attached to mounting frame 808. Motor 860 is connected totransmission shaft 700. Switch 840 is integrated into handle 817 and isconnected to motor 860 through wire 850. Switch 840 activates anddeactivates motor 860. Motor 860 is connected to power source such as arechargeable lithium ion battery or another renewable power supply asknown in the art

Motor 860 rotates transmission shaft 700 between 15,000 to 20,000 rpm.In another preferred embodiment, motor 860 has variable speeds and speedof motor 860 is modulated through use of switch 840.

Conical section 814 is connected to handle post 811. Handle post 811integrally supports saw guide post 812. Saw guide post 812 isperpendicular to the longitudinal axis of saw 802. Handle post 811 isrigidly attached to spindle shaft 800. Shoulder 822 is positionedbetween handle post 811 and guide body 795. Guide body 795 is free torotate with respect to handle post 811 and spindle shaft 800.

Transmission hole 815 extends through handle 817, conical section 814,handle post 811 and spindle shaft 800.

Transmission shaft 700 extends through transmission hole 815.Transmission shaft 700 is kept in position within transmission hole 815by bushings 880. Transmission shaft 700 extends beyond spindle shaft 800and into transmission housing 725.

Guide body 795 has spindle hole 810 which transverses the longitudinalaxis of guide body 795. Spindle shaft 800 fits within spindle hole 810.Spindle hole 810 allows rotation of spindle shaft 800 about thelongitudinal axis of guide body 795. Transmission shaft 700 extendsthrough washer 670 and nut 680 into transmission housing 725.

FIG. 22 a illustrates the mechanics inside transmission housing 725.Bearings 710 and 712 maintain position of transmission shaft 700 withintransmission housing 725 while allowing it to rotate. Transmission shaft700 terminates in bevel gear 735. Thrust bushing 709 is affixed betweenbevel gear 735 and bearing 712 and constrains the axial movement oftransmission shaft 700. Bevel gear 735 meshes with bevel gear 610creating 90 degree transmission. Other transmission schemes, such as aflexible cable, will suffice in other embodiments.

Bevel gear 610 is rigidly integrally connected to bearing shaft 620.Bearing shaft 620 is rigidly integrally connected to frustroconicalsection 637 which is rigidly integrally connected to jaws 650 of chuck660. Mill bit 750 is inserted into jaws 650. The position of chuck 660with respect to transmission housing 725 is maintained by bearings 740and 730 and thrust bushing 708. Mill bit 750 is parallel to saw guidepost 812.

FIGS. 23 a and 23 b are further illustrations of chuck 660. Bevel gear610 is integrally connected to bearing shaft 620. Bearing shaft 620 isintegrally connected to jaws 650. Jaws 650 are approximately cylindricalin shape with mill bit hole 882 removed which is same shape as end ofmill bit 750. Jaws 650 have set screw hole 640. Set screw hole 640 isthreaded to mate with set screw 630.

In one embodiment, mill bit hole 882 has flat surface 642 andsemicircular surface 641. Set screw hole 640 is centered along thelatitudinal axis of flat surface 642.

Referring to FIGS. 22 a and 22 b, mounting plate 720 is attached totransmission housing 725 through use of screws 722. Mounting plate 720has set screw hole 770. Set screw hole 770 allows access to set screw630 for locking mill bit 750 into chuck 660. Mounting plate 720 has bitstop 836 and mounting bracket 835.

Referring now to FIG. 22 b, guide body 795 includes horizontal stop 780and vertical stop 790. Horizontal stop 780 extends from top 782 of guidebody 795 and has horizontal surface 787. Vertical stop 790 is alignedwith bottom 783 of guide body 795. Vertical stop 790 and horizontal stop780 cooperate with bit stop 836 to limit the rotation of thetransmission housing and the mill bit to 90 degrees between a verticalposition and a horizontal position.

When handle 817 is turned counter-clockwise with respect to thelongitudinal axis of guide body 795, bit stop 836 is rotatedcounterclockwise until bit stop 836 abuts saw guide vertical stop 790.Mill bit 750 will be substantially perpendicular to guide body 795 whenbit stop 836 abuts guide vertical stop 790. When handle 817 is rotatedclockwise with respect to the longitudinal axis of guide body 795, bitstop 836 will rotate clockwise until bit stop 836 abuts horizontal stop780. When bit stop 836 abuts horizontal stop 780, mill bit 750 will besubstantially parallel to guide body 795.

In use, mill bit 750 is inserted into mill bit hole 882. Set screw 630is advanced through set screw hole 770, into set screw hole 640 untilabuts mill bit 750. Saw 802 is then inserted into a distractor asdescribed in previous embodiment. Switch 840 activates motor 860 byconnecting it to a power source, which rotates transmission shaft 700and bevel gear 735. Rotation of bevel gear 735 rotates bevel gear 610and chuck 660, which causes mill bit 750 to rotate. Handle 817 ismanually rotated counterclockwise around the longitudinal axis of guidebody 795 which rotates mill bit 750 in relation to the longitudinal axisof guide body 795 and exposing mill bit 750 to vertebrae in order to cuta slot in the vertebra. After a slot has been cut, handle 817 ismanually rotated clockwise around the longitudinal axis of guide body795 until mill bit 750 is substantially parallel to latitudinal axis ofguide body 795. Switch 840 then deactivates motor 860. The procedure isrepeated for cutting additional slots in vertebra as previouslydescribed with manual saw embodiment.

Mill bit 750 has a diameter of between approximately 1 mm and 5 mm and alength of between 0.6 cm and 3.9 cm and corresponds to the size of theradial anchors of the implant being inserted between vertebra. Multiplesize mill bits are included and the appropriate size is inserted tocorrespond to size needed for the particular implant.

In some spondylolisthesis conditions, the relocation of vertebra mayeither be minor or unnecessary, however the natural tilt and locationbetween two adjacent vertebrae needs to be maintained and stabilized.For this type of condition, another embodiment of an implant andinstrumentation are used which includes a tapering to match the tilt ofthe vertebrae.

FIGS. 24 a and 24 b are illustrative of an additional preferredembodiment of a tapered implant. Implant 845 has an implant body 853that is tapered creating a frustroconical shape. Implant body 853 hasimplant body front end 870 and back end 861. The cross-section of frontend 870 is circular. The cross-section of back end 861 is circular.Degree of tapering 875 is the degree by which the tapering occurs alongimplant body 853 and ranges between approximately 2 and 10 degrees.

Implant body 853 has two halves, upper half 862 and lower half 864.Upper half 862 and lower half 864 meet at implant seam 855.

Implant body 853 has radial anchors 876 and 877 on upper half 862 andradial anchors 878 and 879 on lower half 864. Radial anchors 876, 877,878, and 879 are substantially perpendicular to implant seam 855. Radialanchors 878 and 876 have less surface area than radial anchors 877 and879, and are reduced in area to conform to a modified distractor asshown in FIG. 25. Other features of implant 845 are similar to thosepreviously described in other embodiment.

FIG. 25 is illustrative of other preferred embodiments for a distractorand impactor to be used with tapered implant 845. FIG. 25 illustratesimpactor 950 within distractor 940.

Distractor 940 has distractor arm 895 and distractor arm 892. Distractorarm 895 extends longitudinally from side 955 of distractor 940.Distractor arm 892 extends longitudinally from side 945 of distractor940. Distractor arm 895 has taper arm 890 which tapers both the top andbottom between an approximate 2 and 10 degree angle along thelongitudinal axis of distractor arm 895. Taper arm 897 on distractor arm892 tapers the height from both the top and the bottom between anapproximate 2 and 10 degree angle. Taper arm 897 includes distractorstop 910 and taper arm 890 has distractor stop 906. The remainingfeatures of distractor 940 are consistent with previously disclosedembodiment of distractor.

Impactor 950 has impactor head 911. The posterior end of impactor head911 has tapered end 898. Tapered end 898 has between approximately 2 and10 degrees of taper along the longitudinal axis of impactor head 911.Tapered end 898 ends in impactor seat 920 and on either side of impactorseat 920 are stop surfaces 930 and 931. The tapering of tapered end 898corresponds to the tapering of taper arm 890 and taper arm 897 such thatstop surfaces 930 and 931, when fully inserted, touch distractor stop906 and distractor stop 910 and do not extend beyond edges of distractorarms 892 or 895. The remaining features of impactor 950 are consistentwith previously disclosed embodiment of impactor.

As disclosed with prior embodiments, with the tapered implant system,the implant, distractor, impactor, and other parts necessary to completethe disclosed surgery have a variety of heights depending on the patientand the condition to be resolved.

1. A method of correcting a spondylolisthesis condition comprising:providing a linearly adjustable implant having a set of diametricallyopposed radial fins perpendicular to a longitudinal axis of the implant;creating an insert hole in a disk between a pair of affected vertebrae;creating a set of offset diametrically opposed receiver slots in thepair of affected vertebrae; inserting the implant into the hole;rotating the implant about the longitudinal axis to rotate the set ofdiametrically opposed radial fins into the set of offset diametricallyopposed receiver slots; and, linearly adjusting the implant so that thediametrically opposed radial fins move the affected vertebrae.
 2. Themethod of claim 1 wherein the step of inserting further comprises:inserting a distractor having a bilateral wedge surface into the holeand adjacent the pair of affected vertebrae; and, inserting the implantthrough a channel in the distractor to a functional position between thepair of affected vertebrae.
 3. The method of claim 2 wherein the step ofrotating further comprises: coaxially attaching a remote inserter to theimplant before inserting the implant and rotating the remote inserterabout the longitudinal axis of the implant.
 4. The method of claim 2further comprising the step of: choosing the distractor from a pluralityof distractors where each of the plurality of distractors has adifferent height.
 5. The method of claim 2 further comprising: insertinga rotatable saw through the channel in the distractor; rotating therotatable saw, constrained by a set of guide slots in a saw guide, tocreate the offset opposed receiver slots.
 6. The method of claim 5comprising the further step of choosing the saw guide from a pluralityof saw guides where each saw guide of the plurality of saw guides has adifferently spaced set of guide slots.
 7. The method of claim 1 whereinthe step of linearly adjusting the implant further comprises turning aset screw within the implant to effect a displacement of thediametrically opposed radial fins.
 8. The method of claim 1 furthercomprising the steps of: attaching a cover plate to the affectedvertebra, and, attaching an access bolt to the implant through a hole inthe cover plate.
 9. An implant for correcting a spondylolisthesiscondition comprising: a cylindrical body having a first set of radialplanar anchors and a second set of radial planar anchors; the first setof radial planar anchors and the second set of radial planar anchorsrigidly attached to the cylindrical body in a set of parallel planes;each of the set of parallel planes being perpendicular to a longitudinalaxis of the cylindrical body; the first set of radial planar anchorsbeing linearly adjustable along the longitudinal axis of the cylindricalbody with respect to the second set of radial planar anchors.
 10. Theimplant of claim 9 wherein the cylindrical body further comprises a setscrew, coaxial with the longitudinal axis of the cylindrical body forlinearly adjusting the first set of radial planar anchors with respectto the second set of radial planar anchors,
 11. The implant of claim 9wherein: each of the first set of radial planar anchors has a widthequal to a cross-sectional diameter of the cylindrical body; and each ofthe second set of radial planar anchors has a width equal to thecross-sectional diameter of the cylindrical body.
 12. The implant ofclaim 9 wherein the first set of radial planar anchors comprises tworadial planar anchors and the second set of radial planar anchorscomprises two radial planar anchors.
 13. The implant of claim 9 whereinthe first set of radial planar anchors comprises a plurality radialplanar anchors and the second set of radial planar anchors comprise aplurality radial planar anchors.
 14. The implant of claim 13 wherein thefirst set of radial planar anchors comprises a different number ofradial planar anchors than the second set of radial planar anchors. 15.The implant of claim 9 wherein each radial planar anchor of the firstset of radial planar anchors and the second set of radial planar anchorsis comprised of one of the group of titanium, stainless steel,demineralized bone matrix, collagen, ceramic, cement and polymer.
 16. Amethod for correcting alignment between two vertebrae due tospondylotisthesis comprising of the steps: providing a distractor havinga distractor body with a hollow chamber along a distractor bodylongitudinal axis, an anterior end, a posterior end having a firstlongitudinal extension and a second longitudinal extension which extendfrom the distractor body in the direction of the distractor bodylongitudinal axis, the first longitudinal extension having a first stopsurface perpendicular to the first longitudinal extension and extendingparallel to the distractor body, the second longitudinal extensionhaving a second stop surface perpendicular to the second longitudinalextension and extending parallel to the distractor body, a gap betweenthe first stop surface and the second stop surface, a measurement scalealong the first longitudinal extension, and a torque handleperpendicularly attached to the distractor body; providing an impactorhaving an impactor handle, an impactor body having a longitudinal axis,a latitudinal axis, an impactor body anterior end, and an impactor bodyposterior end, the impactor handle being centered on the latitudinalaxis of the impactor body anterior end, an impactor seat centered alongthe latitudinal axis of the impactor body posterior end; providing agate having a gate longitudinal axis, a gate latitudinal axis, adistractor end and a-guide end, the distractor end having an insertionconduit and having a distractor stop, the guide end having a guideconduit, a top side, a bottom side, a right side, a left side, a gateanterior end, a first set of a guide slots from a first centerline ofthe right side to a second centerline of the bottom side and parallel tothe gate anterior end, a second set of guide slots from a thirdcenterline of the left side to a fourth centerline of the top side andparallel to the gate anterior end, a first side slot along the firstcenterline of the right side and ductedly connected to the first set ofguide slots and terminating in a first end, a second side slot along thesecond centerline of the left side and ductedly connected to the secondset of guide slots and terminating in a second end, the first set ofguide slots having a first set spacing and the second set of guide slotshaving a second set spacing, the first set spacing related to the secondset spacing by a third set spacing; providing a saw unit with a sawlongitudinal axis, the saw unit having a handle joined to a spindleconnected to a saw blade, a saw guide body, and a saw guide projection,the saw guide projection joined to the handle at an angle generallyperpendicular to the saw longitudinal axis, the saw guide body furtherhaving a longitudinal pivot hole coaxial with the saw longitudinal axis,the guide body further having a horizontal blade stop and a verticalblade stop, the spindle rotatively mounted in the longitudinal pivothole, the saw blade having a saw blade longitudinal axis parallel to thesaw guide projection and movable between a stoppage position adjacentthe horizontal blade stop and an operational position adjacent thevertical blade stop; providing an implant having a first half having afirst half longitudinal axis, a first half outer surface, and a firstdove-tail joint and a second half having a second half longitudinalaxis, a second half outer surface, and a second dove-tailed joint, thefirst half and the second half slidably connected by first dove-tailedjoint and second dove-tailed joint forming a cylindrical body and acylindrical collar, the first half having a first channel and the secondhalf having a second channel such that when the first half and thesecond half are connected the first channel and the second channel forman implant chamber in the cylindrical body and the cylindrical collar, adrive screw located inside the implant chamber, the first channel beingthreaded, the first half having a first set of radial anchors radiallyextending and generally perpendicular to the first half longitudinalaxis from the first half outer surface and the second half having asecond set of radial anchors radially extending from the second halfouter surface and generally perpendicular to the second halflongitudinal axis, the cylindrical collar having an outside perimeter,and the outside perimeter of the cylindrical collar being threaded;providing an inserter having a top half and a bottom half, the top halffurther having a top longitudinal axis and a top joint along the toplongitudinal axis, the top half having a first semi-cylindrical sectionand a first semi-hexagonal section, the bottom half having a bottomlongitudinal axis and a bottom joint along the bottom longitudinal axis,the bottom half having a second semi-cylindrical section and a secondsemi-hexagonal section, the top half and the bottom half slidinglyconnected along the top joint and the bottom joint and create acylindrical section and a hexagonal section, the top half having aconnection end, the connection end having a threaded connection channel;providing a guide block having a guide block longitudinal axis, a topcap connected to an insertion bottom, and an inserter hole centeredalong the guide block longitudinal axis; providing a nut having a nuthead and a nut body, the nut body being generally perpendicular to thenut head, the nut body having an implant hole, the implant hole beingthreaded; providing a plate having a plate hole, a plurality of screwholes, and a face, the plate hole being centered in the face; exposing amisaligned first vertebra, a misaligned second vertebra, and a diskbetween the misaligned first vertebra and the misaligned second vertebraof a patient through an anterior surgical approach; identifying aputative midline of the disk; marking the putative midline on the disk;removing a portion of the disk forming an opening in the disk; insertingthe impactor through the hollow chamber of the distractor until theimpactor body posterior end abuts the first stop surface and the secondstop surface; aligning the posterior end with the putative midline onthe disk and the opening; striking the impactor handle until theposterior end is aligned with the first misaligned vertebra's dorsalepiphyseal ring; removing the impactor from the distractor leaving thedistractor between the misaligned first vertebra and the misalignedsecond vertebra; inserting the distractor end of the gate over theanterior end of the distractor until the anterior end abuts thedistractor stop; inserting the saw unit through the insertion conduit ofthe gate and the hollow chamber of the distractor until the saw guideprojection abuts the first end of the first side slot; creating a firstslot in the misaligned first vertebra by directing the saw guideprojection into a first guide slot of the first set of guide slots byrotating the handle and causing the saw blade to rotate from thestoppage position to the operation position and back to the stoppageposition; repeating the previous step for each guide slot of the firstset of guide slots thereby creating a first set of vertebra slots;removing the saw unit from the gate and the distractor; rotating the sawunit 180 degrees about the saw longitudinal axis; reinserting the sawunit through the insertion conduit of the gate and the hollow chamber ofthe distractor until the saw guide projection abuts the second end ofthe second side slot; creating a second slot in the misaligned secondvertebra by directing the saw guide projection into a first guide slotof the second set of guide slots by rotating the handle and causing thesaw blade to rotate from the stoppage position to the operation positionand back to the stoppage position; repeating the previous step for eachguide slot of the second set of guide slots and creating a second set ofvertebra slots; removing the saw unit from the gate and the distractor;removing the gate from the distractor; turning the drive screw until thefirst set of radial anchors and the second set of radial anchors areconsistent with the third set spacing; inserting the inserter throughthe inserter hole; connecting the connection end to the cylindricalcollar; inserting the inserter and the guide block through the hollowchamber of the distractor until the top cap abuts the anterior end ofthe distractor; rotating the inserter to lodge the first set of radialanchors in the first set of vertebra slots and lodge the second set ofradial anchors in the second set of vertebra slots; removing theinserter connection end from the cylindrical collar; removing theinserter and the guide block from the hollow chamber; removing thedistractor; turning the drive screw to align the misaligned firstvertebra and the misaligned second vertebra; performing interbodyarthrodesis around the implant; placing the nut body through the platehole; connecting the nut to the implant by threading the implant hole inthe nut body onto the cylindrical collar of the implant; and inserting aplurality of screws into the misaligned first vertebra and themisaligned second vertebra through the plurality of screw holes.
 17. Themethod of claim 16 further comprising the steps of: placing a pin insidethe disk to determine the putative midline; and taking radiographs toconfirm the putative midline.
 18. The method of claim 16 furthercomprising the steps of: marking the opening in the disk with a scalpel.19. The method of claim 16 further comprising the steps of: determiningthe amount of misalignment between the misaligned first vertebra and themisaligned second vertebra by use of one of the group of radioagraphs,and MRI.
 20. The method of claim 16 further comprising the steps of:determining degree of misalignment between the misaligned first vertebraand the misaligned second vertebra by use of the measurement scale. 21.The method of claim 16 further comprising the steps of: removing theplurality of screws from the misaligned first vertebra and themisaligned second vertebra; removing the nut body from the implant;rotating the drive screw; placing the nut body through the plate hole;connecting the nut to the implant by threading the implant hole onto thecylindrical collar of the implant; and inserting the plurality of screwsthrough the plurality of screw holes into the misaligned first vertebraand the misaligned second vertebra.
 22. The method of claim 16 furthercomprising the steps of: rotating the drive screw clockwise 360 degreesthereby moving the first implant half relation to the second implanthalf by a single millimeter.
 23. The method of claim 16 furthercomprising the steps of: rotating the drive screw counter-clockwise 360degrees thereby moving the first implant half in relation to the secondimplant half by a single millimeter.
 24. The method of claim 16 furthercomprising the steps of: rotating the drive screw to align themisaligned first vertebra and the misaligned second vertebra until thefirst set of radial anchors and the second set of radial anchors arevertically aligned.
 25. The method of claim 16 further comprising thesteps of: placing the connection end of the top half of the inserter onthe cylindrical collar; and sliding the bottom half of the inserter inrelation to the top half of the inserter until the bottom half abuts thesecond implant half.
 26. The method of claim 16 further comprising thesteps of: removing the bottom half away from the second implant half;and rotating the inserter 90 degrees around the top latitudinal axis.27. The method of claim 16 further comprising the steps of: providingthe saw unit having a motor which rotates a transmission, and the sawblade having a mill bit connected to the transmission; activating themotor to rotate the mill bit.
 28. An implant for changing an alignmentbetween two vertebrae and maintaining the alignment comprising: a firsthalf having a first body with a first longitudinal axis, a first collar,a first chamber, a first joint, a first longitudinal side and a firstset of radial anchors; the first set of radial anchors radiallyextending generally perpendicularly from the first body; a second halfhaving a second body with a second longitudinal axis, a second collar, asecond chamber, a second joint, a second longitudinal side and a secondset of radial anchors; the second set of radial anchors radiallyextending generally perpendicularly from the second body; the first halfand the second half slidingly connected by the first joint and thesecond joint along the first longitudinal side and the secondlongitudinal side; the first body and the second body connected form animplant body; the first collar and the second collar connected form animplant collar; the first chamber and the second chamber connected forman implant chamber; the first chamber being threaded with a first set ofthreads; a drive screw having an outside perimeter and a spanner head;the outside perimeter being threaded with a second with a set ofthreads; the drive screw located in the implant chamber; the first setof threads in engagement with the second set of threads; the first setof threads and the second set of threads having a pre-determinedrelationship to allow the first half to move a pre-determined distancein relation to the second half when the drive screw is rotated apre-determined angle of rotation; the first set of radial anchors andthe second set of radial anchors being generally parallel; the first setof radial anchors having a first set of corners and a second set ofcorners; and, the second set of radial anchors having a third set ofcorners and a fourth set of corners.
 29. The implant of claim 28 whereinthe second set of corners and the third set of corners are rounded. 30.The implant of claim 28 wherein the pre-determined distance is about 1mm for the pre-determined angle of rotation of about 360 degrees. 31.The implant of claim 28 wherein the pre-determined distance is about 0.5mm for the pre-determined angle of rotation of about 360 degrees. 32.The implant of claim 28 wherein the first set of radial anchors includesa first plurality of anchors.
 33. The implant of claim 32 wherein thesecond set of radial anchors includes a second plurality of anchors. 34.The implant of claim 28 wherein the implant is constructed of one of thegroup of titanium, stainless steel, demineralized bone matrix, collagen,ceramic, cement and polymer.
 35. The implant of claim 28 wherein theimplant body has a front cross-section and a back cross-section, thefront cross-section being circular and the back cross-section beingcircular; the front cross-section connected to the back cross-section bya generally cylindrical surface having a taper; and the taper having aset incline.
 36. The implant of claim 35 wherein the set incline isbetween about 2 degrees and about 10 degrees.
 37. A system forcorrecting alignment between two vertebrae caused by spondylotisthesiscomprising: a distractor having a distractor body with a hollow chamberalong a distractor body longitudinal axis, an anterior end, a posteriorend having first a first longitudinal extension and a secondlongitudinal extension which extend from the distractor body in thedirection of the distractor body longitudinal axis, the firstlongitudinal extension having a first stop surface perpendicular to thefirst longitudinal extension and extending parallel to the distractorbody, the second longitudinal extension having second stop surfaceperpendicular to the second longitudinal extension and extendingparallel to the distractor body, a gap between the first stop surfaceand the second stop surface, a measurement scale along the firstlongitudinal extension, and a torque handle perpendicularly attached tothe distractor body; an impactor having an impactor handle, an impactorbody having a longitudinal axis, a latitudinal axis, an impactor bodyanterior end, and an impactor body posterior end, the impactor handlebeing centered on the latitudinal axis of the impactor body anteriorend, an impactor seat centered along the latitudinal axis of theimpactor body posterior end; the impactor seat fits within the gap onthe distractor; a gate having a gate longitudinal axis, a gatelatitudinal axis, a distractor end and a guide end, the distractor endhaving an insertion conduit and having a distractor stop, the guide endhaving a guide conduit, a top side, a bottom side, a right side, a leftside, a gate anterior end, a first set of a guide slots from a firstcenterline of the right side to a second centerline of the bottom sideand parallel to the gate anterior end, a second set of guide slots froma third centerline of the left side to a fourth centerline of the topside and parallel to the gate anterior end, a first side slot along thefirst centerline of the right side and ductedly connected to the firstset of guide slots and terminating in a first end, a second side slotalong a second centerline of the left side and ductedly connected to thesecond set of guide slots and terminating in a second end, the first setof guide slots having a first set spacing and the second set of guideslots having a second set spacing, the first set spacing related to thesecond set spacing by a third set spacing; a saw unit with a sawlongitudinal axis, the saw unit having a saw handle jointed to spindleconnected to a saw blade, a saw guide body, and a saw guide projection,the saw guide projection joined to the handle at an angle generallyperpendicular to the saw longitudinal axis, the saw guide body furtherhaving a longitudinal pivot hole coaxial with the saw longitudinal axis,the guide body further having a horizontal blade stop and a verticalblade stop, the spindle rotatively mounted in the longitudinal pivothole, the saw blade having a saw blade longitudinal axis parallel to thesaw guide projection and movable between a stoppage position dictated bythe horizontal blade stop and an operational position dictated by thevertical blade stop; an implant having a first half having a first bodywith a longitudinal axis, a first collar, a first chamber, a firstjoint, a first longitudinal side and a first set of radial anchors, thefirst set of radial anchors radially extending generally perpendicularlyfrom the first body, a second half having a second body with a secondlongitudinal axis, a second collar, a second chamber, a second joint, asecond longitudinal side and a second set of radial anchors, the secondset of radial anchors radially extending generally perpendicularly fromthe second body, the first half and the second half slidably connectedby the first joint and the second joint along the first longitudinalside and the second longitudinal side, the first body and the secondbody connected form an implant body, the first collar and the secondcollar connected form an implant collar, the first chamber and thesecond chamber connected form an implant chamber, the first chamberbeing threaded with a first set of threads, a drive screw having anoutside perimeter and a spanner head, the outside perimeter beingthreaded with a second set of threads, the drive screw located in theimplant chamber, the first set of threads in engagement with the secondset of threads, the first set of threads and the second set of threadshaving a pre-determined relationship to allow the first half to move apre-determined distance in relation to the second half when the drivescrew is rotated a pre-determined angle of rotation, the first set ofradial anchors and the second set of radial anchors being generallyparallel, the first set of radial anchors having a first set of cornersand a second set of corners, and the second set of radial anchors havinga third set of corners and a fourth set of corners. an inserter having atop half and a bottom half, the top half further having a toplongitudinal axis and a top joint along the top longitudinal axis, thetop half having a first semi-cylindrical section and a firstsemi-hexagonal section, the bottom half having a bottom longitudinalaxis and a bottom joint along the bottom longitudinal axis, the bottomhalf having a second semi-cylindrical section and a secondsemi-hexagonal section, the top half and the bottom half slidinglyconnected along the top joint and the bottom joint and create acylindrical section and a hexagonal section, the top half having aconnection end, the connection end having a threaded connection channel;the threaded connection channel having a fourth pitch; the third pitchof the collar perimeter matching the fourth pitch of the threadedconnection channel; a guide block having a guide block longitudinalaxis, a top cap connected to an insertion bottom, and an inserter holecentered through the guide block longitudinal axis; a nut having a nuthead and a nut body, the nut body being generally perpendicular to thenut head, the nut body having a threaded implant hole, the threadedimplant hole having fifth pitch; the third pitch of the collar perimetermatching the fifth pitch of the threaded implant hole; and a platehaving a plate hole, a plurality of screw holes, and a face, a back, andthe plate hole having a face diameter and a back diameter.
 38. Thesystem of claim 37 wherein the first set of radial anchors includes onefrom the group of one anchor, two anchors, three anchors, four anchors,five anchors.
 39. The system of claim 37 wherein the second set ofradial anchors includes one from the group of one anchor, two anchors,three anchors, four anchors, five anchors.
 40. The system of claim 37wherein the distractor, the impactor, the gate, the saw unit, and theimplant are constructed from one of the group of titanium, and stainlesssteel.
 41. The system of claim 37 wherein the face diameter is largerthan the back diameter.
 42. The system of claim 37 wherein the firstimplant half further comprises a first set of alignment marks and thesecond implant half further comprises a second set of alignment marksand the first set of alignment marks when the first set of radialanchors is parallel with the second set of radial anchors.
 43. Thesystem of claim 37 wherein the hollow chamber of the distractor has across-section and the cross-section is one of the group of rectangular,square, and elliptical.
 44. The system of claim 37 wherein the firststop surface has a first posterior end and the second stop surface has asecond posterior end, and the first posterior end and the secondposterior end are rounded.
 45. The system of claim 37 wherein the nuthead has a rotational insert, and the rotation insert has the shape ofone of the group of hexagonal, and spanner.
 46. The system of claim 37wherein the gate has a pointing means for indicating a gate orientation.47. The system of claim 37 wherein the measurement scale has a pluralityof markings spaced 1 mm apart.
 48. The system of claim 37 wherein theimpactor handle has a centerline which is parallel to a horizontal axisof the impactor body.
 49. The system of claim of claim 37 wherein thefirst longitudinal extension having a first tapering end and the secondlongitudinal extension having a second tapering end, the first taperingend tapering in height by a set tapering degree, and the second taperingend tapering in height by the set tapering degree; and the impactor bodyhaving a tapering end, the tapering end tapering in height by the settapering degree.
 50. The system of claim 49 wherein the set taperingdegree is between about 2 degrees and about 10 degrees.
 51. The systemof claim 37 wherein the saw unit includes a handle housing, a motorrigidly mounted in the handle housing, a drive shaft extending from anddriven by the motor, the drive shaft extending through a hole in thehandle housing and the spindle, a transmission housing rigidly attachedto the spindle, a transmission located within the transmission housing,the transmission operatively connected to the drive shaft and to achuck; the chuck releasably fixed to a mill bit; the transmissionhousing further comprising an index means for limiting the rotation ofthe transmission housing with respect to the guide body.
 52. The systemof claim 51 wherein the transmission includes a plurality of bevelgears.
 53. An implant for changing an alignment between two vertebraecomprising: a first body member having a first central longitudinalchannel adjacent a first dovetail joint; a first set of radial anchorsextending from the first body member generally perpendicular to thefirst central longitudinal chamber; a second body member having a secondcentral longitudinal channel adjacent a second dovetail joint, thesecond set of radial anchors extending from the second body generallyperpendicular to the second central longitudinal chamber; the first bodymember and the second body member slidingly connected by the firstdovetail joint and the second dovetail joint whereby the first centrallongitudinal chamber and the second central longitudinal chamber form acylindrical chamber; the first central longitudinal chamber including athreaded receiving surface; and, a threaded set screw in the cylindricalchamber and engaging the threaded receiving surface.
 54. The implant ofclaim 53 wherein each radial anchor of the first set of radial anchorshas a first set of rounded corners; and, wherein each radial anchor ofthe second set of radial anchors has a second set of rounded corners.55. The implant of claim 53 wherein the threaded set screw and thethreaded receiving surface cooperate to move the first set of radialanchors about one millimeter with respect to the second set of radialanchors when the threaded set screw is rotated about 360 degrees about alongitudinal axis.
 56. The implant of claim 53 wherein the threaded setscrew and the threaded receiving surface cooperate to move the first setof radial anchors about one millimeter with respect to the second set ofradial anchors when the threaded set screw is rotated about 720 degreesabout a longitudinal axis.
 57. The implant of claim 53 wherein the firstset of radial anchors and the second set of radial anchors include apredetermined number of radial anchors, said predetermined number beingone of the group of one, two, three, four and five.
 58. A system oftools for inserting an implant for correcting a spondylotisthesiscondition between two affected vertebrae comprising: a distractor havinga distractor body with a hollow chamber along a distractor bodylongitudinal axis, an anterior end, a posterior end having first a firstlongitudinal extension and a second longitudinal extension which extendfrom the distractor body in the direction of the distractor bodylongitudinal axis, the first longitudinal extension having a first stopsurface perpendicular to the first longitudinal extension and extendingparallel to the distractor body, the second longitudinal extensionhaving a second stop surface perpendicular to the second longitudinalextension and extending parallel to the distractor body, a gap betweenthe first stop surface and the second stop surface, and a torque handleattached to the distractor body; an impactor having a striking end and aposterior end; the impactor fitting within the hollow chamber of thedistractor; a gate with a gate longitudinal axis, a gate latitudinalaxis, a distractor end and a guide end, the distractor end having aninsertion conduit and having a distractor stop, the guide end having aguide conduit, a first side, a second side, a third side, a fourth side,a gate anterior end, a first set of a guide slots from centerline of thefourth side to centerline of the second side and parallel to the gateanterior end, a second set of guide slots from centerline of the thirdside to centerline of the first side and parallel to the gate anteriorend, a third guide slot along centerline of the fourth side and ductileconnected to the first set of guide slots and terminating in a firstend, a fourth guide slot along centerline of the fourth side and ductileconnected to the second set of guide slots and terminating in a secondend, the first set of guide slots having a first set spacing and thesecond set of guide slots having a second set spacing, the first setspacing related to the second set spacing by a third set spacing; theanterior end of the distractor fitting within the insertion conduit butnot within the guide conduit a saw unit with a saw longitudinal axis,the saw unit having a handle joined to a spindle connected to a sawblade, a saw guide body, and a saw guide projection, the saw guideprojection joined to the handle at an angle perpendicular to the sawlongitudinal axis, the saw guide body further having a longitudinalpivot hole coaxial with the longitudinal axis, the spindle rotativelymounted in the longitudinal pivot hole, the saw blade movable between astoppage position and an operational position; the saw guide bodyfitting within the guide conduit of the gate and the hollow chamber ofthe distractor; an implant adapted to be fitted between the affectedvertebrae having a first half having a first half longitudinal axis, afirst half outer surface, and a first joint and a second half having asecond half longitudinal axis, a second half outer surface, and a secondjoint, the first half and the second half connected by the first jointand the second joint forming an implant body, the first half having afirst channel and the second half having a second channel such that whenthe first half and the second half are connected the first channel andthe second channel form an implant chamber in the implant body, a drivebolt located inside the implant chamber having a first set of threads,the first channel being threaded, a second set of threads, the firsthalf having a first set of radial anchors extending perpendicularly fromthe first half outer surface and the second half having a second set ofradial anchors extending perpendicularly from the second half outersurface; the first set of threads engaging the second set of threads; aninserter having a top half and a bottom half, the top half having a toplongitudinal axis and a top joint along the top longitudinal axis, thebottom half having a bottom longitudinal axis and a bottom joint alongthe bottom longitudinal axis, the top half and the bottom half slidinglyconnected along the top joint and the bottom joint, the top half havinga connection end, the connection end releasably connectable to theimplant body; a nut having a nut head and a nut body, the nut body beingperpendicular to the nut head, the nut body having an implant hole,releasably connectable to the implant body; a plate connectable to thetwo affected vertebrae having a plate hole through which passes the nutbody.
 59. The system of claim 58 wherein the implant body has a set ofalignment marks on the first implant half and the second implant half.60. The system of claim 58 wherein the gate has a pointing means fortactically discerning a direction of insertion.
 61. The system of claim58 wherein the distractor has a measurement scale along the firstlongitudinal extension.
 62. The system of claim 58 where the impactorhas an impactor handle, an impactor body having a longitudinal axis, alatitudinal axis, an impactor body anterior end, and an impactor bodyposterior end, the impactor handle being centered on the latitudinalaxis of the impactor body anterior end, an impactor seat centered alongthe latitudinal axis of the impactor body posterior end; the impactorseat fits within the gap on the distractor.
 63. The system of claim 58where the guide body further having a horizontal blade stop and avertical blade stop.
 64. The system of claim 58 further comprising aguide block having a guide block longitudinal axis, a top cap connectedto an insertion bottom, and an inserter hole centered through the guideblock longitudinal axis; the insertion bottom fitting into the hollowchamber.
 65. The system of claim 58 further comprising a set of gateswherein each gate in the set of gates has a different third set spacing.66. The system of claim 58 further comprising a set of distractors,wherein each distractor of the set of distractors has a unique height.67. The system of claim 58 further comprising a set of impactors,wherein each impactor of the set of impactors has a unique height. 68.The system of claim 58 further comprising a set of saw units, whereineach saw unit of the set of saw units has a unique height.
 69. Thesystem of claim 58 further comprising a set of saw guide bodies, whereineach saw guide body of the set of saw guide bodies has a unique height.70. The system of claim 58 further comprising a set of implants, each ofthe set of implant bodies having a unique diameter.
 71. The system ofclaim of claim 58 wherein the first longitudinal extension has a firsttapering end and the second longitudinal extension has a second taperingend, the first tapering end tapering in height by a set tapering degree,and the second tapering end tapering in height by the set taperingdegree; and the impactor having an impactor body, the impactor bodyhaving a tapering end, the tapering end tapering in height by the settapering degree.
 72. The system of claim 71 wherein the set taperingdegree is between about 2 degrees and about 10 degrees.
 73. The systemof claim 58 wherein the saw unit having a handle housing, a motorrigidly mounted in the handle housing, a drive shaft connected anddriven by the motor, the drive shaft extending through a longitudinalhole in the handle housing and the spindle, a transmission housingrigidly attached to the spindle; a transmission located within thetransmission housing, the transmission operatively connected to thedrive shaft and to a chuck, the chuck releasably fixed to a mill bit,the transmission housing further comprising an index means for limitingthe rotation of the transmission housing with respect to the guide body.74. The system of claim 73 wherein the transmission comprising aplurality of bevel gears.
 75. A system of tools for inserting an implantfor correcting a spondylolisthesis condition between two affectedvertebrae comprising: a distractor having a distractor body with ahollow chamber along a distractor body longitudinal axis, an anteriorend, a posterior end having first a first longitudinal extension and asecond longitudinal extension which extend from the distractor body inthe direction of the distractor body longitudinal axis, the firstlongitudinal extension having a first tapering end and a first stopsurface perpendicular to the first longitudinal extension and extendingparallel to the distractor body, the second longitudinal extensionhaving a second tapering end and a second stop surface perpendicular tothe second longitudinal extension and extending parallel to thedistractor body, the first tapering end and the second tapering endtapering in height by a set tapering degree; a gap between the firststop surface and the second stop surface, and a torque handle attachedto the distractor body; an impactor having a striking end, a posteriorend, and an impactor body, the impactor body having a tapering end, thetapering end tapering in height by the set tapering degree; the impactorfitting within the hollow chamber of the distractor; a gate with a gatelongitudinal axis, a gate latitudinal axis, a distractor end and a guideend, the distractor end having an insertion conduit and having adistractor stop, the guide end having a guide conduit, a first side, asecond side, a third side, a fourth side, a gate anterior end, a firstset of a guide slots from centerline of the fourth side to centerline ofthe second side and parallel to the gate anterior end, a second set ofguide slots from centerline of the third side to centerline of the firstside and parallel to the gate anterior end, a third guide slot alongcenterline of the fourth side and ductedly connected to the first set ofguide slots and terminating in a first end, a fourth guide slot alongcenterline of the fourth side and ductedly connected to the second setof guide slots and terminating in a second end, the first set of guideslots having a first set spacing and the second set of guide slotshaving a second set spacing, the first set spacing related to the secondset spacing by a third set spacing; the anterior end of the distractorfitting within the insertion conduit but not within the guide conduit asaw unit with a saw longitudinal axis, the saw unit having a handlejoined to a spindle, the handle having a handle housing, a motor rigidlymounted in the handle housing, a drive shaft connected to and driven bythe motor, the drive shaft extending through a hole in the handlehousing and the spindle, a saw guide projection joined to the handle atan angle perpendicular to the saw longitudinal axis, the saw guide bodyfurther having a longitudinal pivot hole coaxial with the longitudinalaxis, the spindle rotatively mounted in the longitudinal pivot hole, atransmission housing rigidly attached to the spindle; a transmissionlocated within the transmission housing, the transmission operativelyconnected to the drive shaft and to a chuck; the chuck releasably fixedto a mill bit; the transmission housing further comprising an indexmeans for limiting the rotation of the transmission housing with respectto the guide body, the mill bit movable between a stoppage position andan operational position; the saw guide body fitting within the guideconduit of the gate and the hollow chamber of the distractor; an implantadapted to be fitted between the two affected vertebrae having a firsthalf having a first half longitudinal axis, a first half outer surface,and a first joint and a second half having a second half longitudinalaxis, a second half outer surface, and a second joint, the first halfand the second half connected by the first joint and the second jointforming an implant body, the implant body further having a frontcross-section and a back cross-section, the front cross-section beinggenerally circular and the back cross-section being generally circular;the front cross-section connected to the back cross-section by agenerally cylindrical surface with a taper; the taper having a setincline, the first half having a first channel and the second halfhaving a second channel such that when the first half and the secondhalf are connected the first channel and the second channel form animplant chamber in the implant body, a drive bolt located inside theimplant chamber having a first set of threads, the first channel beingthreaded, a second set of threads, the first half having a first set ofradial anchors extending substantially perpendicularly from the firsthalf outer surface and the second half having a second set of radialanchors extending substantially perpendicularly from the second halfouter surface; the first set of threads engaging the second set ofthreads; an inserter having a top half and a bottom half, the top halfhaving a top longitudinal axis and a top joint along the toplongitudinal axis, the bottom half having a bottom longitudinal axis anda bottom joint along the bottom longitudinal axis, the top half and thebottom half slidingly connected along the top joint and the bottomjoint, the top half having a connection end, the connection endreleasably connectable to the implant body; a nut having a nut head anda nut body, the nut body being perpendicular to the nut head, the nutbody having an implant hole, releasably connectable to the implant body;a plate connectable to the two affected vertebrae having a plate holethrough which passes the nut body.
 76. The system of claim 75 whereinthe implant body further comprises a set of indexing marks on the firstimplant half and the second implant half.
 77. The system of claim 75wherein the gate further comprises a pointing means for tacticallydiscerning a direction of insertion.
 78. The system of claim 75 whereinthe distractor further comprises a measurement scale along the firstlongitudinal extension.
 79. The system of claim 75 where the impactorhas an impactor handle, the impactor body having a longitudinal axis, alatitudinal axis, an impactor body anterior end, and an impactor bodyposterior end, the impactor handle being centered on the latitudinalaxis of the impactor body anterior end, an impactor seat centered alongthe latitudinal axis of the impactor body posterior end; the impactorseat engaging the gap on the distractor.
 80. The system of claim 75where the guide body further comprising a horizontal blade stop and avertical blade stop.
 81. The system of claim 75 further comprising aguide block having a guide block longitudinal axis, a top cap connectedto an insertion bottom, and an inserter hole centered through the guideblock longitudinal axis; the insertion bottom fitting into the hollowchamber.
 82. The system of claim 75 further comprising a set of gateswherein each gate in the set of gates has a different third set spacing.83. The system of claim 75 further comprising a set of distractors,wherein each distractor of the set of distractors has a unique height.84. The system of claim 75 further comprising a set of impactors,wherein each impactor of the set of impactors has a unique height. 85.The system of claim 75 further comprising a set of saw units, whereineach saw unit of the set of saw units has a unique height.
 86. Thesystem of claim 75 further comprising a set of saw guide bodies, whereineach saw guide body of the set of saw guide bodies has a unique height.87. The system of claim 75 further comprising a set of implants, each ofthe set of implant bodies having a unique diameter.
 88. The system ofclaim 75 wherein the transmission comprising a plurality of bevel gears.89. The implant of claim 75 wherein the set incline is between about 2degrees and about 10 degrees.
 90. The system of claim 75 wherein the settapering degree is between about 2 degrees and about 10 degrees.